Summary of Work: Age is associated with a slowing of movement and loss of strength. At a critical level this can be an important factor leading to functional disability in the elderly. The natural history of how these changes occur and the causes are poorly understood. During the past year, we have further explored the contribution of nerve function to age associated loss of strength using data collected from the BLSA in 1967-1970. Age associated muscle strength loss is attributed to decreasing muscle mass. Both strength and mass are dependent on muscle innervation. Median and, to a lesser extent, ulnar nerves are the major nerves supplying grip strength. Median but not ulnar nerve significantly related to grip strength along with age and forearm circumference. We used path analysis to investigate the relationships between age, median nerve, physical activity and forearm circumference (as an estimate of arm muscle mass) on grip strength. Each of these had independent contributions to grip strength. In addition, age, and physical activity directly influenced forearm circumference. Furthermore, the effect of age appeared to differ in younger versus older men. Motor nerves, muscle mass and age have significant, independent contributions to age associated levels of strength. Further analyses are under way in association with our project "Effects of Age on Muscle Strength, Body Composition and Health Status," to understand the time course of these changes.